FIELD OF THE INVENTION

The invention relates to a transmission for a bicycle.

BACKGROUND TO THE INVENTION

The invention relates to a transmission for a bicycle. The transmission can include:

- an input formed by a crank axle and an output connectable to a front sprocket of the bicycle,

a housing connected or connectable to a frame of the bicycle, a planetary gear set with at least three rotational members of which a first rotational member is connected to the crank axle, a second rotational member is connected to the output, and a third rotational member is connected to the housing,

a sensor between the third rotational member and the housing, and an electric motor having a stator connected to the housing and a rotor connected to the output.

The sensor can be a force sensor, a position sensor or a displacement sensor, such as a rotation sensor. From a measured sensor value a torque can be calculated that is transmitted to the housing. The electric motor is for supporting the cyclist. Thereto, a control unit can control the electric motor as a function of the calculated torque.

Such transmission is known from DE 10 2011 089559 A. In electric bicycles direct drive motors are used at the front wheel or at the rear wheel. Rear wheel hub motors provide the best driveability. A drawback of rear wheel hub motors is that no gear hub can be used. It is possible to use a derailleur. However, in case of gearing down at an incline, the torque that the electric motor can apply directly to the wheel remains the same, while actually a higher support torque from the motor is desired. In order to solve this, the electric motor can be connected to the crank axle, as in the known transmission. Thus, both gear hubs and derailleurs can be applied. A further advantage is that the torque of the electric motor is amplified towards the rear wheel in case of gearing down.

A common chain transmission reduces the torque to the rear wheel by a factor of two, and a common gear hub can amplify the torque by a factor of maximum two. Hence, as a result the torque of the electric motor directly coupled to the crank axle is not amplified towards the rear wheel in the common situation in the lowest gear. To solve this, the front sprocket can be reduced in size by a factor of two which results in a factor two increase of torque at the rear wheel from the electric motor. However, this increases the rotational speed of the front sprocket by a factor of two and a reducing transmission is required between the front sprocket and the crank axle (so increasing from the crank axle to the front sprocket). A concentric transmission, such as a planetary gear set, is useful for this.

Because a torque measurement of the crank axle torque (not the motor torque) is required, the planetary gear set is also very well equipped for measuring the torque by means of a force on the stationary (non-rotating) rotational member.

A factor two increasing planetary gear set is difficult to construct when the ring wheel is fixed, the planet carrier is connected to the input and the sun gear is connected to the output, as is the case in the known transmission, because then the transmission between the ring wheel and the sun wheel needs to be equal to one, i.e. that the diameter of the ring wheel needs to be equal to the diameter of the sun wheel. Further it can be difficult to control the output torque when there is no direct or sufficiently accurate control of the derailleur or hub transmission in relation with the electric motor torque. SUMMARY OF THE INVENTION

It is an object to provide a transmission as described in the preamble wherein, in a simpler way than in the known transmission, a first planetary gear set can be constructed with a relatively large transmission ratio (preferably equal to or larger than two) between the first and second rotational members.

Thereto, the transmission is characterized in that the third rotational member is formed by a planet carrier.

Optionally, at least a part of the third rotational member is part of the housing. Optionally, one or more planet shafts are connected to the planet carrier and/or housing.

Optionally, the sensor is connected to the carrier, and/or the housing, and/or one or more of the planet shafts.

With a planetary gear set with double planets a transmission ratio between the ring wheel and the sun wheel of two (or more) is required (increasing speed toward the sun wheel), which can be constructed properly, for example with the ring wheel being connected to the input and the sun wheel being connected to the output. The output speed will be higher than the input speed. Further, it is also possible to achieve this with a planetary gear set with two sun gears or two ring gears and one planet carrier. In both constructions the pedaling torque can be measured by measuring the torque on the stationary planet carrier or on the planet shaft(s) connected to the housing or on the housing in which the shafts are connected.

Optionally, the transmission is arranged such that the second rotational member is formed by a sun gear.

Optionally, the transmission is arranged such that the first rotational member is formed by a further sun gear.

Optionally, the transmission is arranged such that the first rotational member is formed by a ring gear.

Optionally, the planet carrier includes a plurality of planet gear pairs. The planet gears of each pair can be rotationally coupled. The planet gears of each pair can mesh with each other. One of the meshing planet gears of the pair can mesh with the ring gear. The other one of the meshing planet gears of the pair can mesh with the sun gear. The planet gears of each pair can be coaxially rotationally fixed. One of the rotationally fixed planet gears of the pair can mesh with the sun gear. The other one of the rotationally fixed planet gears of the pair can mesh with the further sun gear.

The known transmissions can have a further disadvantage in that the electric motor rotates at a high rotational speed and is coupled to the crank axle or chain ring via one or more toothed gears. This can cause sound production.

According to an aspect, the transmission can be arranged such that the electric motor is directly connected to the crank axle or chain ring. Hence, the electric motor can rotate at a low rotational speed without toothed gears intervening between the electric motor and the crank axle or chain ring. The invention is however not limited to a direct connection of the electric motor to the chain ring.

According to a further aspect, a sub -transmission is integrated in the transmission. With the additional sub -transmission the speed ratio between the crank and the wheel can be regulated. Further advantage is that the crank shaft, electric motor, sub -transmission and torque sensor can all be integrated in one housing that can be mounted to the bicycle frame, and no further hub transmission or derailleur system is needed. However still a hub/wheel transmission and/or derailleur can be combined with the system.

Optionally, the sub-transmission includes torque transfer elements and at least one sub-transmission input and one sub-transmission output. The sub- transmission input can be connected to the output of the first planetary gear set and the sub-transmission output can be connected to the input of a chain / belt drive of the bicycle, e.g. to a front sprocket.

Optionally, the sub-transmission is embodied as a stepped gear transmission.

Optionally, the sub-transmission is embodied as a continuously variable transmission.

Optionally, the sub-transmission is embodied as a second planetary gear set with at least three rotational members, wherein a first rotational member is connected to the output of the first planetary gear set, a second rotational member is connected to the input of the chain/belt transmission, and a third rotational member is connected to a torque reaction element, such as the housing and/or electric motor.

According to a further aspect, the sub -transmission is embodied as the second planetary gear set and the electric motor is connected to one of the rotational members of the second planetary gear set.

Optionally, the electric motor is connected to the third rotational member of the second planetary gear set.

Optionally, a first clutch and/or a first freewheel is connected between the third rotational member of the second planetary gear set and the housing. Optionally, a second clutch and/or a second freewheel is connected between two of the rotational members of the second planetary gear set.

Optionally, the first rotational member of the second planetary gear set is a sun gear. Optionally the second rotational member of the second planetary gear set is a planet carrier. Optionally, the third rotational member of the second planetary gear set is an annulus / ring gear.

An advantage is that the power of the crank input will be amplified towards the wheel with increasing bicycle speed above a certain wheel speed by the electric motor. This will enable a constant high acceleration of the bicycle with a constant low input torque and speed. This will give a progressive acceleration feel to the rider.

Optionally, using the first clutch / freewheel and/or the second clutch / freewheel a selectable fixed gear ratio can be made with the second planetary gear set.

Optionally, an overrunning bearing or an overrunning clutch is connected between the crank axle and the first rotational member of the first planetary gear set, and/or between the output and the second rotational member of the first planetary gear set, and/or between the output and the electric motor.

Optionally, the output is formed by a hollow axle. Optionally, the hollow output axle is concentric with the crank axle.

Optionally, the sensor includes one or more of a force sensor, a position sensor, a displacement sensor, and a rotation sensor.

Optionally, the transmission includes a calculation unit arranged for calculating the torque that is transmitted to the housing on the basis of a measurement value of the sensor.

According to an aspect is provided a bicycle including a transmission as described above.

Optionally, the bicycle includes a control unit arranged for controlling the electric motor as a function of the measured sensor value and/or the calculated torque.

According to an aspect is provided a method for determining a torque applied to a crank axle of a bicycle using a sensor. The sensor is arranged between a third rotational member and a housing of a transmission having an input formed by the crank axle, and an output connected to a front sprocket / chain ring of the bicycle, the housing being connected to a frame of the bicycle. The transmission has a first planetary gear set having at least three rotational members, wherein a first rotational member is connected to the crank axle, a second rotational member is connected to the output and the third rotational member is connected to the housing, and an electric motor with a stator connected to the housing and a rotor connected to the output, wherein the third rotational member is formed by a planet carrier. The method further includes determining the torque on the basis of a measured value of the sensor. The sensor can be arranged for measuring one or more of force, position, displacement, and rotation.

According to an aspect is provided a method for supporting a cyclist. The method includes determining a torque applied by the cyclist to a crank axle of a bicycle as described above. The method also includes controlling the electric motor of the bicycle as a function of the calculated torque.

It will be appreciated that any one or more of the above aspects, features and options can be combined. It will be appreciated that any one of the options described in view of one of the aspects can be applied equally to any of the other aspects. It will also be clear that all aspects, features and options described in view of the transmission apply equally to the bicycle and the methods, and vice versa.

BRIEF DESCRIPTION OF THE DRAWING

The invention will further be elucidated on the basis of exemplary embodiments which are represented in a drawing. The exemplary embodiments are given by way of non-limitative illustration. It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting example.

In the drawing:

Fig. 1 shows a schematic representation of a transmission; Fig. 2 shows a simplified schematic cross sectional view of the transmission according to Fig. 1;

Fig. 3 shows a modular variety of the transmission of Fig. 1 in assembled state; Fig. 4 shows the modular variety of Fig. 3 in separate modules;

Fig. 5 shows a modular variety of the transmission of Fig. 1 in separate modules;

Fig. 6 shows a simplified schematic representation of a cross sectional view of a transmission;

Fig. 7 shows a schematic representation of a transmission;

Fig. 8 shows a simplified schematic representation of a transmission;

Fig. 9 shows the transmission of Fig. 8 in separate modules;

Fig. 10 shows a variety of the transmission of Fig. 8 in separate modules;

Fig. 11 shows a schematic representation of a transmission; Fig. 12 shows a schematic representation of a transmission; and

Fig. 13 shows a schematic representation of a transmission. DETAILED DESCRIPTION

Figure 1 shows a schematic representation of a transmission 1. The transmission 1 includes an input, here formed by a crank axle 3. The transmission 1 includes an output 5. In this example, the output 5 is connected to a front sprocket 7 of a bicycle. Here, the front sprocket 7 is coupled to a rear sprocket 11 via a chain or belt 9. Here the rear sprocket 11 is coupled to a wheel hub 15 via an overrunning bearing 13.

In this example, the crank axle 3 is connected to a planetary gear set 19 via a second overrunning bearing 17. It will be appreciated that it is also possible that alternatively the second overrunning bearing 17 is coupled between the planetary gear set 19 and the output 5. The planetary gear set 19 includes three rotational members. A first rotational member 21 is connected to the crank axle. A second rotational member 23 is connected to the output 5. A third rotational member 25 is connected to a housing (not shown in Figure 1) which is connected to frame 27 (schematically shown) of the bicycle.

Between the third rotational member 25 and the housing a torque sensor 29 is mounted for measuring a torque exerted to the crank axle 3 via the pedals 31. Further, an electric motor 33 is included, e.g. in the housing. The electric motor 33 is coupled to the output 5 via a third overrunning bearing 35. The electric motor is arranged for supporting the cyclist. Thereto, a control unit (not shown) controls the electric motor, here as a function of the torque measured by the torque sensor 29.

Figure 2 shows a simplified schematic representation of a cross sectional view of a transmission 1 according to Figure 1. Here it can clearly be seen that the stator 39 of the electric motor 33 is connected to the housing 37 and that the rotor 41 of the electric motor 33 is connected to the output 5 via the third overrunning bearing 35. The rotor 41 is received in the housing 37 via bearing 43. The crank axle 3 is received in the housing 37 via bearing 45 and the bearings 47 and 49. Here, the output 5 is formed by a hollow axle received between the bearings 47 and 49. In this example, the third rotational member 25 is formed by a planet carrier PC. In this example, the second rotational member 23 is formed by the sun gear SI. In this example, the first rotational member 21 is formed by a further sun gear S2.

In the example of Figure 2, the planet carrier PC is connected to the housing 37. Hence, the planet carrier PC is stationary. Here, the sun gear SI is connected to the output 5. Here the further sun gear S2 is connected to the crank axle 3. Here, the planet carrier PC includes one or more planet gear pairs P1,P2. The planet gears PI, P2 of each pair are rotationally coupled. Here the planet gears of each pair are coaxially coupled. In this example, a first planet gear P2 of the pair meshes with the further sun gear. A second planet gear PI of the pair here meshes with the sun gear SI.

Figure 3 shows a modular variety of a transmission 1 according to Figure I. The housing 37 includes two parts 37a, 37b. The first housing part 37a is connected to the frame 27. The second housing part 37b houses the bearing 49. The first and second housing parts 37a, 37b can be connected to each other, e.g. by means of fasteners such as bolts. In this example, the rotor 41 includes two parts 41a, 41b. Here, the first rotor part 41a is connected to the magnets 42. Here, the second rotor part 41b is connected to the third overrunning bearing 35. In this example, the first and second rotor parts 41a, 41b are connected through a spline connection 51. The spline connection 51 includes a first spline connection part 51a and a second spline connection part 51b. Hence, the first and second rotor parts 41a, 41b can be connected and disconnected in a sliding fashion. In Figure 4 the transmission is separated into a first transmission module la and a second transmission module lb. The first transmission module la here includes the first housing part 37a, the first rotor part 41a and the first spline connection part 51a. Here the second transmission module lb includes the second housing part 37b, the second rotor part 41b and the second spline connection part 51b. Here, the torque sensor 29 and the bearing 45 are included by the first transmission module la. Here, the crank axle 3 and the hollow output axle 5 are included by the second transmission module lb. Also, in this example, the planet carrier PC, planet gear pair(s) PI, P2, sun gear SI and further sun gear S2 are included by the second transmission module lb. Between the torque sensor 29 and the third rotational member, here the planet carrier PC, a coupling 53 is included. The coupling 53 is arranged such that sliding the second transmission module lb into the first transmission module la, will rotationally couple the parts 53a, 53b of the coupling 53 included by the first and second transmission modules,

respectively. Similarly, sliding the second transmission module lb out of the first transmission module la, will decouple the coupling 53.

Figure 5 shows a variety of a transmission 1 according to Figure 1 in separate modules la, lb. The first transmission module la here includes the first housing part 37a, the first rotor part 41a and the first spline connection part 51a. Here the second transmission module lb includes the second housing part 37b, the second rotor part 41b and the second spline connection part 51b. Here, the crank axle 3 and the hollow output axle 5 are included by the second transmission module lb. Also, in this example, the planet carrier PC, planet gear pair(s) PI, P2, sun gear SI and further sun gear S2 are included by the second transmission module lb. In this example, the torque sensor 29 and the bearing 45 are included by the second transmission module lb. Here the second transmission module lb includes an auxiliary member 54. The auxiliary member 54 can connect to the first housing part 37a, e.g. via a spline connection 56. A first spline connection part 56a is then included by the first transmission module la and a second spline connection part 56b is then included by the second transmission module lb.

Figure 6 shows a simplified schematic representation of a cross sectional view of a transmission 55. In this transmission 55, the electric motor 33 is positioned not concentrically but eccentrically relative to the crank axle 3. Here, the rotor 41 is connected to the third overrunning bearing 35 via a secondary transmission 57. The secondary transmission 57 can be any type of transmission, such as a gear wheel transmission, chain transmission and/or belt transmission.

Figure 7 shows a schematic representation of a transmission 59. In the transmission 59 the planetary gear set 19' is different. Here the planetary gear set 19' includes a sun gear S and a ring gear R instead of two sun gears SI, S2 and a planet carrier PC. The planet gears Pa, Pb are provided between the sun gear S and the ring gear R in pairs.

Figure 8 shows a simplified schematic representation of a cross section of a transmission 59 according to Figure 7. The first rotational member 21' of the planetary gear set 19' is here formed by a ring gear R. The second rotational member 23' of the planetary gear set 19' is here formed by a sun wheel S. The third rotational member 25' of the planetary gear set 19' is here formed by a planet carrier PC to which the planet gears Pa, Pb are connected in pairs. The torque sensor 29' here is positioned against the stator 39 instead of against the housing 37.

In Figures 9 and 10 two examples of transmissions in separated modules are shown with different locations of the torque sensor 29.

In Figure 9, the transmission 59 includes a first transmission module 59a and a second transmission module 59b. The first housing part 59a is connected to the frame 27. The second housing part 59b houses the bearing 49. The first and second housing parts 59a, 59b can be connected to each other, e.g. by means of fasteners such as bolts. In this example, the rotor 41 includes two parts 41a, 41b. The first rotor part can e.g. be connected to the magnets. Here, the second rotor part 41b is connected to the third overrunning bearing 35. In this example, the first and second rotor parts 41a, 41b are connected through a spline connection 51. The spline connection 51 includes a first spline connection part and a second spline connection part. Hence, the first and second rotor parts 41a, 41b can be connected and disconnected in a sliding fashion. The first transmission module 59a here includes the first housing part 37a, the first rotor part 41a and the first spline connection part. Here the second transmission module 59b includes the second housing part 37b, the second rotor part 41b and the second spline connection part. Here, the crank axle 3 and the hollow output axle 5 are included by the second transmission module 59b. Also, in this example, the planet carrier PC, planet gears Pa, Pb, and the sun gear S are included by the second transmission module 59b. In this example, the torque sensor 29 and the bearing 45 are included by the second transmission module 59b. In Figure 9, the torque sensor 29' is positioned against the stator 39. Here the second transmission module 59b includes an auxiliary member 54 ^' . The auxiliary member 54' can connect to the first housing part 37a, e.g. via a spline connection. A first spline connection part is then included by the first transmission module 59a and a second spline connection part is then included by the second transmission module 59b.

In Figure 10, the transmission 59' includes a first transmission module

59'a and a second transmission module 59'b. In Figure 10, the first transmission module 59'a includes the first housing part 37a, the first rotor part 41a and the first spline connection part 51a. Here the second transmission module 59'b includes the second housing part 37b, the second rotor part 41b and the second spline connection part 51b. Here, the torque sensor 29 and the bearing 45 are included by the first transmission module 59'a. In Figure 10 the torque sensor 29' is positioned against the housing 37. Here, the crank axle 3 and the hollow output axle 5 are included by the second transmission module 59'b. Also, in this example, the planet carrier PC, planet gears Pa, Pb, and the sun gear S are included by the second transmission module 59'b. Between the torque sensor 29 and the third rotational member, here the planet carrier PC, a coupling 53' is included. The coupling 53' is arranged such that sliding the second transmission module 59'b into the first transmission module 59'a, will rotationally couple the parts 53'a, 53'b of the coupling 53' included by the first and second transmission modules, respectively. Similarly, sliding the second transmission module 59'b out of the first transmission module 59'a, will decouple the coupling 53'.

Figure 11 shows a schematic representation of a transmission 60. The transmission 60 includes a first planetary gear set 19, e.g. as described in view of Figures 1-10. In Figure 11 the transmission 60 further includes a sub -transmission 61. The sub-transmission 61 includes torque transfer elements and at least one sub -transmission input 62 and one sub-transmission output 63. Here the sub- transmission input 62 is connected to the output 5 of the first planetary gear set 19. Here the sub-transmission output 63 is connected to the input of the chain / belt drive 9 of the bicycle, e.g. to a front sprocket. The chain / belt drive 9 is coupled to a wheel hub 15 via an overrunning bearing (not shown). In the example of Figure 11, the electric motor 33 is connected to a second input 64 of the sub -transmission 61. The sub-transmission 61 can e.g. be a stepped gear transmission or a continuously variable transmission.

Figure 12 shows a schematic representation of a transmission according to Figure 11. In Figure 12 the sub-transmission 61 is embodied as a second planetary gear set. Here, the second planetary gear set 61 includes at least three rotational members. In this example, a first rotational member is connected to the output 5 of the first planetary gear set 19. In this example, a second rotational member is connected to the input of the chain/belt transmission 9. In this example, a third rotational member is connected to the housing 37 (schematically shown), e.g. via a first lock-up clutch or freewheel B. Here, the electric motor 33 is connected to the output 5 of the first planetary gear set 19, e.g. as described in view of Figures 1-10. The second planetary gear set 61 can include a second lock-up clutch / freewheel C between two rotational members of the second planetary gear set 61 (three possible locations shown in Figure 12). Hence, using the first clutch / freewheel B and/or the second clutch / freewheel C a selectable fixed gear ratio can be made with the second planetary gear set 61. In an example, the first rotational member of the second planetary gear 61 set is a sun gear, the second rotational member of the second planetary gear set is a planet carrier, and the third rotational member of the second planetary gear set is an annulus / ring gear.

Figure 13 shows a schematic representation of a transmission according to Figure 11. In Figure 13 the sub-transmission 61 is embodied as a second planetary gear set. Here, the second planetary gear set 61 includes at least three rotational members. In this example, a first rotational member is connected to the output 5 of the first planetary gear set 19. In this example, a second rotational member is connected to the input of the chain/belt transmission 9. In this example, a third rotational member is connected to the housing 37 (schematically shown), e.g. via a first lock-up clutch or freewheel B. The second planetary gear set 61 here includes a second lock-up clutch / freewheel C between two rotational members of the second planetary gear set 61 (three possible locations shown in Figure 12). Hence, using the first clutch / freewheel B and/or the second clutch / freewheel C a selectable fixed gear ratio can be made with the second planetary gear set 61. Here, the electric motor 33 is connected to one of the rotational members of the second planetary gear set 61. Here, the electric motor 33 is connected to the third rotational member of the second planetary gear set 61. In an example, the first rotational member of the second planetary gear 61 set is a sun gear, the second rotational member of the second planetary gear set is a planet carrier, and the third rotational member of the second planetary gear set is an annulus / ring gear.

Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various

modifications, variations, alternatives and changes may be made therein, without departing from the essence of the invention.

For example, in the example of Figure 6 the eccentrically located electric motor is applied in a transmission similar to the transmission shown in Figure 5. It will be appreciated that the eccentrically located electric motor can also be applied in a transmission similar to Figures 1-4 or 7- 10.

For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however,

alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged and understood to fall within the framework of the invention as outlined by the claims. The specifications, figures and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense. The invention is intended to embrace all alternatives, modifications and variations which fall within the spirit and scope of the appended claims. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage.